This invention relates to color monitors adapted to receive analog R, G and B color input signals.
The market for television monitors has grown rapidly with the proliferation of computers and computer terminals. A monitor is simply a television receiver without a tuner and associated signal processing circuits required to receive, demodulate and process transmitted television signals. The monitor directly accepts video information and applies it to a picture tube. Most monitors are monochrome, that is, they only accept monochrome signals and include picture tubes having faceplates covered with a single type light-emitting phosphor, rather than different colored light-emitting phosphors. While the particular phosphor may produce colored light (such as green or blue) the entire display is monochromatic.
Color monitors are desirable because of their greater ability to present meaningful information. They are, of course, more complex, requiring individual color signal channels and a color picture tube capable of generating different colored light outputs in response to appropriate color signal inputs. Few user controls, other than a brightness control for regulating the amount of light emitted from the display, are required. A brightness control on a monochrome monitor is simple to incorporate. Putting a brightness control on a color monitor is more complicated because of the relationship between the primary colors, which determines the color balance of the display, and the need to maintain proper color saturation with changes in contrast and brightness of the display.
The television industry has over many years developed all types of controls for adjusting picture brightness, contrast, color saturation, hue, tint, etc. The consensus appears to be that, in addition to color saturation and tint controls, a black level control and a so-called picture control, the latter for adjusting color amplitude and picture contrast together, are most suited for producing pleasing displays.
In a conventional color television receiver, wideband brightness information and narrow band color difference information are processed in separate luminance and chrominance channels and subsequently matrixed to form the red, green and blue (RGB) color signals applied to the color picture tube. The wide band luminance signal may be separately controlled to affect black level, brightness and contrast and the narrow band chrominance signals are similarly controlled to affect color level and tint.
Color monitors however, may not have separate chrominance channel and luminance channel inputs. Rather, wideband R G and B color signals are supplied as inputs. The problem of providing black level and picture controls for wideband R G B signals is substantial. There have been very simple controls provided for monitors capable of accepting digital R G B color signals, but even these results are very limited in terms of the range of colors available. The manner of application of those simple controls to color monitors adapted to receive R G B analog signals is not apparent.